[issue-87][apollo-java]: Added a new feature to get instance count by namespace.

CHANGES.md

@@ -11,6 +11,7 @@ Apollo 2.5.0
 * [Feature: Provide a new open API to return the organization list](https://github.com/apolloconfig/apollo/pull/5365)
 * [Refactor: Exception handler adds root cause information](https://github.com/apolloconfig/apollo/pull/5367)
 * [Feature: Enhanced parameter verification for edit item](https://github.com/apolloconfig/apollo/pull/5376)
+* [Feature: Added a new feature to get instance count by namespace.](https://github.com/apolloconfig/apollo/pull/5381)
 
 ------------------
 All issues and pull requests are [here](https://github.com/apolloconfig/apollo/milestone/16?closed=1)

apollo-portal/src/main/java/com/ctrip/framework/apollo/openapi/server/service/ServerInstanceOpenApiService.java

@@ -0,0 +1,37 @@
+/*
+ * Copyright 2024 Apollo Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+package com.ctrip.framework.apollo.openapi.server.service;
+
+import com.ctrip.framework.apollo.openapi.api.InstanceOpenApiService;
+import com.ctrip.framework.apollo.portal.environment.Env;
+import com.ctrip.framework.apollo.portal.service.InstanceService;
+import org.springframework.stereotype.Service;
+
+@Service
+public class ServerInstanceOpenApiService implements InstanceOpenApiService {
+
+    private final InstanceService instanceService;
+
+    public ServerInstanceOpenApiService(InstanceService instanceService) {
+        this.instanceService = instanceService;
+    }
+
+    @Override
+    public int getInstanceCountByNamespace(String appId, String env, String clusterName, String namespaceName) {
+        return instanceService.getInstanceCountByNamespace(appId, Env.valueOf(env), clusterName, namespaceName);
+    }
+}

apollo-portal/src/main/java/com/ctrip/framework/apollo/openapi/v1/controller/InstanceController.java

@@ -0,0 +1,36 @@
+/*
+ * Copyright 2024 Apollo Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+package com.ctrip.framework.apollo.openapi.v1.controller;
+
+import com.ctrip.framework.apollo.openapi.api.InstanceOpenApiService;
+import org.springframework.web.bind.annotation.*;
+
+@RestController("openapiInstanceController")
+@RequestMapping("/openapi/v1/envs/{env}")
+public class InstanceController {
+    private final InstanceOpenApiService instanceOpenApiService;
+
+    public InstanceController(InstanceOpenApiService instanceOpenApiService) {
+        this.instanceOpenApiService = instanceOpenApiService;
+    }
+
+    @GetMapping(value = "/apps/{appId}/clusters/{clusterName}/namespaces/{namespaceName}/instances")
+    public int getInstanceCountByNamespace(@PathVariable String appId, @PathVariable String env,
+                                           @PathVariable String clusterName, @PathVariable String namespaceName) {
+        return this.instanceOpenApiService.getInstanceCountByNamespace(appId, env, clusterName, namespaceName);
+    }
+}